chore: ignore SQLite temporary files and database files

- Add SQLite WAL and SHM file patterns to gitignore
- Include main database files to prevent accidental commits
- Ensures database state doesn't get committed to version control

.gitignore

@@ -222,3 +222,8 @@ zig-out/
 # Experiment data (local testing)
 experiments/
 data/
+
+# SQLite temporary files
+db/*.db-shm
+db/*.db-wal
+db/*.db